Our original proposal that cyclic GMP plays a role in the regulation of macromolecular synthesis at a specific time in the cell cycle of bacteria remains as a viable hypothesis. We will continue to measure intracellular levels of cyclic GMP in synchronized cells in an effort to further relate the kinetics of the "transient pulses of synthesis" to cell cycle events. In these studies, wild type E. coli B will be utilized as well as studies with dna A and dna P (ts) strains, env A and env B strains, min A and min B strains and several lon strains. All of these strains are presently in the lab: most were sent to us by Barbara Bachman. Since both cyclic GMP requiring mutants that we had for a few weeks formed filaments in the absence of cyclic GMP, it is suggested that cyclic GMP may be involved in DNA synthesis initiation of termination or in septum formation. Naladixic acid inhibits termination and causes filament formation. Penicillin, at low concentration, produces filamentous cells but does not inhibit nucleic acid synthesis. We will measure cyclic GMP in cells treated with these two agents to determine their effect on the timing or amount of synthesis. In addition, we will continue our search for temperature sensitive mutants of E. coli K-12 and B that require cyclic GMP for normal growth.